[Damien]

Water is a byproduct of the combustion of gasoline and oxygen, so that is fine. There is also some condensation in the exhaust due to temperature fluctuations.

With having the truck run a little rich, you are making more power as you stated. With the more power, you do not need as much throttle so you are saving gas. If you run the engine lean and it is struggling, you are going to need more throttle to get up to speed, and therefore need more fuel.